Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/30—Electroplating: Baths therefor from solutions of tin
  • C25D3/32—Electroplating: Baths therefor from solutions of tin characterised by the organic bath constituents used
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
  • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
  • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
  • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
  • H01L21/28—Manufacture of electrodes on semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/268
  • H01L21/283—Deposition of conductive or insulating materials for electrodes conducting electric current
  • H01L21/288—Deposition of conductive or insulating materials for electrodes conducting electric current from a liquid, e.g. electrolytic deposition
  • H01L21/2885—Deposition of conductive or insulating materials for electrodes conducting electric current from a liquid, e.g. electrolytic deposition using an external electrical current, i.e. electro-deposition
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/56—Electroplating: Baths therefor from solutions of alloys
  • C25D3/60—Electroplating: Baths therefor from solutions of alloys containing more than 50% by weight of tin
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L24/00—Arrangements for connecting or disconnecting semiconductor or solid-state bodies; Methods or apparatus related thereto
  • H01L24/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
  • H01L24/10—Bump connectors ; Manufacturing methods related thereto
  • H01L24/11—Manufacturing methods
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L24/00—Arrangements for connecting or disconnecting semiconductor or solid-state bodies; Methods or apparatus related thereto
  • H01L24/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
  • H01L24/10—Bump connectors ; Manufacturing methods related thereto
  • H01L24/12—Structure, shape, material or disposition of the bump connectors prior to the connecting process
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D21/00—Processes for servicing or operating cells for electrolytic coating
  • C25D21/16—Regeneration of process solutions
  • C25D21/18—Regeneration of process solutions of electrolytes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
  • H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
  • H01L2224/10—Bump connectors; Manufacturing methods related thereto
  • H01L2224/11—Manufacturing methods
  • H01L2224/114—Manufacturing methods by blanket deposition of the material of the bump connector
  • H01L2224/1146—Plating
  • H01L2224/11462—Electroplating
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
  • H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
  • H01L2224/10—Bump connectors; Manufacturing methods related thereto
  • H01L2224/12—Structure, shape, material or disposition of the bump connectors prior to the connecting process
  • H01L2224/13—Structure, shape, material or disposition of the bump connectors prior to the connecting process of an individual bump connector
  • H01L2224/13001—Core members of the bump connector
  • H01L2224/13099—Material
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
  • H01L2924/01—Chemical elements
  • H01L2924/01006—Carbon [C]
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
  • H01L2924/01—Chemical elements
  • H01L2924/01013—Aluminum [Al]
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
  • H01L2924/01—Chemical elements
  • H01L2924/01016—Sulfur [S]
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
  • H01L2924/01—Chemical elements
  • H01L2924/01022—Titanium [Ti]
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
  • H01L2924/01—Chemical elements
  • H01L2924/01023—Vanadium [V]
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
  • H01L2924/01—Chemical elements
  • H01L2924/01029—Copper [Cu]
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
  • H01L2924/01—Chemical elements
  • H01L2924/01033—Arsenic [As]
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
  • H01L2924/01—Chemical elements
  • H01L2924/01041—Niobium [Nb]
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
  • H01L2924/01—Chemical elements
  • H01L2924/01047—Silver [Ag]
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
  • H01L2924/01—Chemical elements
  • H01L2924/01057—Lanthanum [La]
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
  • H01L2924/01—Chemical elements
  • H01L2924/01078—Platinum [Pt]
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
  • H01L2924/01—Chemical elements
  • H01L2924/01082—Lead [Pb]
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
  • H01L2924/013—Alloys
  • H01L2924/0132—Binary Alloys
  • H01L2924/01322—Eutectic Alloys, i.e. obtained by a liquid transforming into two solid phases
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
  • H01L2924/013—Alloys
  • H01L2924/014—Solder alloys

Definitions

• This invention relates to electroplating baths and methods for plating tin-based alloys, and more specifically, the invention relates to tin-silver (Sn-Ag) alloy solder wafer bumping in the manufacture of microelectronic devices.
• Solder wafer bumps conventionally comprise solders of the tin-lead (Sn-Pb) alloy group.
• the Sn-Pb solders may be formed in a variety of compositions including the low melting eutectic comprising 63% Sn and 37% lead. High Sn alloys are called fine solders and are used extensively in electrical work. Many Sn-Pb alloy compositions exhibit broad pasty temperature ranges which enhance their workability.
• a particular problem associated with the use of Ag in Sn-Ag alloy solder wafer bumping is associated with the spontaneous reduction of Ag ions from the electroplating bath.
• Ag ions being very noble, have a tendency toward immersion/displacement plating upon exposure to certain UBM layers, particularly Cu layers. Accordingly, precise control of the Ag ion concentration in the electroplating solution and therefore control of the Ag metal content and uniformity in the Sn-Ag solder wafer bump is rendered difficult.
• There is a need for a plating method which allows for control of the Ag ion content in solution, and thus control of the Ag metal content in the alloy solder wafer bump.
• the present invention is directed to a process for forming a solder bump comprising exposing an under bump metal structure to an electrolytic bath comprising a source of Sn 2+ ions, a source of Ag + ions, and an N-allyl-thiourea compound, and supplying an external source of electrons to the electrolytic bath to deposit a Sn-Ag alloy onto the under bump metal structure.
• the invention is also directed to a process for forming a solder bump comprising exposing an under bump metal structure to an electrolytic bath comprising a source of Sn 2+ ions, a source of Ag + ions, and a quaternary ammonium surfactant; and supplying an external source of electrons to the electrolytic bath to deposit a Sn-Ag alloy onto the under bump metal structure.
• the invention is also directed to a process for forming a solder bump comprising exposing an under bump metal structure to an electrolytic bath comprising a source of Sn 2+ ions, a source of Ag + ions, and an amidinothiourea compound; and supplying an external source of electrons to the electrolytic bath to deposit a Sn-Ag alloy onto the under bump metal structure .
• the invention is directed to a process for forming a Sn-Ag electrolytic bath for deposition of solder bumps, the process comprising combining a source of Ag + ions with a complexor for Ag + ions and water to form a bath precursor comprising Ag complex in a substantial absence of any source of Sn +2 ions ; and adding a source of Sn +2 ions to the bath precursor comprising the Ag complex.
• the invention is directed to an electroplating composition for plating a Sn-Ag solder bump comprising a source of Sn 2+ ions, a source of Ag + ions, an N-allyl-thiourea compound, and a quaternary ammonium surfactant; and also to an electroplating composition for plating a Sn-Ag solder bump comprising a source of Sn 2+ ions ; a source of Ag + ions ; an ainidinothiourea compound; and a quaternary ammonium surfactant .
• FIGS. IA, IB, and 1C are SEM photographs of solder bumps prepared according to the method described in Example 11.
• FIGS. 2A, 2B, and 2C are SEM photographs of reflowed solder bumps prepared according to the method described in Example 12.
• FIG. 3A shows a wafer having a patterned distribution of dies.
• FIG. 3B shows the measurement position of 5 wafer bumps within each die.
• Sn-Ag alloy solder bumps are deposited from an electroplating bath onto an under bump metal structure, such as a silicon wafer substrate overlaid by metallization layers, for use in the manufacture of a microelectronic device.
• an under bump metal structure such as a silicon wafer substrate overlaid by metallization layers
• Sn-Ag alloy solder bumps can be deposited having uniform bump heights, uniform Ag content and distribution in the bumps, and good reflow characteristics.
• the electroplating bath exhibits good stability with respect to Ag immersion/displacement of the Cu under bump metal or soluble Sn anode and plates the Sn-Ag alloy at high current densities.
• the plating baths can plate a Sn-Ag alloy at current densities up to 20 amps per square decimeter (Amp/dm 2 , hereinafter "ASD") with substantially no Ag displacement on Cu UBM or soluble Sn anode.
• ASD amps per square decimeter
• the plating baths plate Sn-Ag alloy bumps with substantially reduced or eliminated voiding between the bumps and Cu UBM.
• the invention is described herein in the context of Sn-Ag alloy solder bumps on microelectronic device substrates, which solder bumps are deposited in patterns to yield, for example, the pattern of as-deposited bumps shown in Figs. IA, IB, and 1C. These bumps are reflowed to yield the pattern of reflowed bumps shown in Figs. 2A, 2B, and 2C.
• the nature of the substrate as an electronic device substrate is not critical to the applicability of the invention.
• the present invention stems from the discovery that certain additives to a Sn-Ag electroplating bath increase Ag + ion stability and allow plating at high current densities.
• the discovered additives substantially reduce the aforementioned problem of spontaneous reduction of Ag + ion onto unintended surfaces, which had detracted from bath stability and uniformity in Sn-Ag proportions in the intended deposits.
• an N-allyl thiourea compound which strongly complexes Ag + ions is included in the bath.
• One particular such compound is an N-allyl-N' -hydroxyalkyl thiourea compound.
• the alkyl group is ethyl
• the hydroxyl group is in the ⁇ position on the ethyl group.
• This compound, N-allyl-N' - ⁇ hydroxyethyl- thiourea is hereinafter referred to as "HEAT" .
• the N- allyl thiourea compound which strongly complexes Ag + ions substantially inhibits Ag + ion displacement onto the Cu UBM and soluble Sn anode.
• Ag + ion stability is enhanced by including in the bath an amidinothiourea compound which also strongly complexes Ag + ions.
• the amidinothiourea compound is amidinothiourea .
• the formation of the stable silver complex reduces the reduction potential closer to that of Sn 2+ , such that the current density is not limited by the otherwise rapid Ag + ion diffusion rate. Instead, the current density is limited by the diffusion rate of Sn 2+ ions, which are present typically in such high concentrations, up to about 50 g/L to about 60 g/L or more, that very high current densities can be employed.
• Selected N-allyl thiourea compounds act to increase the solubility of Ag + ions in the bath by forming complexes with Ag + ions at acidic pH and to inhibit displacement reactions between Ag + ions and Cu UBM or soluble Sn anode.
• N-allyl thiourea compounds shift the Ag + reduction potential closer to the reduction potential of Sn 2+ , allowing for plating at high current densities.
• Exemplary N-allyl thiourea compounds include N-allyl thiourea, and HEAT. In selecting a suitable N-allyl thiourea compound, compounds which are unable to result in a water soluble complex with Ag + ions at acidic pH or are toxic are avoided.
• N-allyl thiourea compounds such as HEAT
• HEAT N-allyl thiourea compounds
• N- allyl thiourea compounds shown below in the following general structure (1) : wherein R 1 , R 2 , R 3 , R 4 , R 5 , and R 6 are each independently H, OH, hydrocarbyl, substituted hydrocarbyl, heterocycloalkyl, substituted heterocycloalkyl, alkoxy, substituted alkoxy, aryl, substituted aryl, heteroaryl, or substituted heteroaryl .
• R 1 , R 2 , R 3 , R 4 , Rs, and R 5 are heterocycloalkyl or heteroaryl
• the ring substituent may comprise 0, S, or N atoms.
• Exemplary substituents on the substituted R groups include halide, hydroxyl, alkoxy, aryl, heteroaryl, nitro, cyano, and mercaptan.
• R 2 , R 3 , R 4 , R 5 , and R 6 are H.
• R 1 , R 2 , R 3 , R 4 , R 5 , and R 6 are H, and the compound is N-allyl thiourea.
• R 2 , R 3 , R 4 , R 5 , and R 6 are H and R 1 is -CH 2 CH 2 OH, and the N-allyl thiourea compound is HEAT, which has the following structure (2) :
• Selected amidinothiourea compounds act to increase the solubility of Ag + ions in the bath by forming complexes with Ag + ions at acidic pH and to inhibit displacement reactions between Ag + ions and Cu UBM or soluble Sn anode.
• a suitable amidinothiourea compound compounds which are unable to result in a water soluble complex with Ag + ions at acidic pH or are toxic are avoided.
• the general formula of suitable amidinothiourea compounds are shown below in the following formula (3) :
• R 8 and R 9 are either S or N, and when R s is S, R 9 is N and when R 8 is N, R 9 is S; and Rio, Rn, Ri2, and Ri 3 are each independently H, OH, hydrocarbyl, substituted hydrocarbyl, heterocycloalkyl, substituted heterocycloalkyl, alkoxy, substituted alkoxy, aryl, substituted aryl, heteroaryl, or substituted heteroaryl .
• Exemplary substituents on the substituted Rio, Rn r Ri 2 , and Ri 3 include halide, hydroxyl, alkyl, alkoxy, aryl, heteroaryl, nitro, cyano, and mercaptan.
• Ri 0 , Rn, R12, and Ri 3 are all hydrogen, and the amidinothiourea compound is amidinothiourea, which has the following structure (4) :
• the concentration of the N-allyl-thiourea compound or amidinothiourea compound is between about 0.5 g/L and about 24 g/L. Employing too much of the compound causes decomposition to free thiourea derivative. Employing too little results in insufficient complexing of Ag.
• the concentration is at least about 1 g/L, such as about 1.4 g/L, about 1.5 g/L, about 1.75 g/L, or about 2.2 g/L. In one embodiment, the concentration is no greater than about 8 g/L, such as about 8 g/L, about 6 g/L, about 4 g/L, or about 3 g/L.
• between about 0.5 g/L and about 16 g/L of HEAT is added to complex Ag + ions and enhance their solubility, while also inhibiting displacement reactions between Ag + ions and Cu UBM or soluble Sn anode.
• between about 0.5 g/L and about 16 g/L, such as between about 1 and about 8 g/L of amidinothiourea is added to complex Ag + ions and enhance their solubility.
• Silver immersion plating also known as “displacement” plating occurs in electroplating baths spontaneously due to high nobility of Ag + ions.
• the reduction of Ag is described by the following reaction:
• E° for the reaction indicates the very positive redox potential of Ag + .
• Cu 2+ and Sn 4+ are less noble than Ag + as shown by the lower reduction potentials of the following reduction reactions :
• Ag + ions spontaneously oxidize Sn 2+ ions to Sn 4+ ions and Cu metal to Cu 2+ ions .
• Ag + ions are reduced to Ag metal, which may become a finely divided metal floating in solution or deposit spontaneously on the substrate, walls of the plating tank, or soluble Sn anode.
• Spontaneous Ag + ion displacement plating renders difficult control of the concentration of Ag + ions in the electroplating bath, which is a severe limitation in the use of Ag in electroplating alloys, such as in Sn-based solder wafer bumps.
• the thiourea compounds such as HEAT and amidinothiourea
• HEAT and amidinothiourea are added to the Sn-Ag electroplating bath to complex Ag + ions and thereby control both the solubility and stability of Ag + ions in the plating bath.
• HEAT and amidinothiourea also lower the reduction potential of Ag + ions, bringing that potential closer to the reduction potential of Sn 2+ ions, which allows for better control of the concentration and uniformity of Ag metal in the Sn-Ag alloy solder wafer bump and allows for plating at high current densities.
• quaternary ammonium surfactants are added to the bath in the currently preferred embodiment .
• the quaternary ammonium surfactants which have been found useful for adding to the plating baths of the present invention include alkyl dimethyl benzyl ammonium salts in which the alkyl group is between 10 and 18 carbons long, preferably the alkyl group is 12 to 14 carbons long.
• the alkyl group may be substituted or unsubstituted.
• a particularly preferred quaternary ammonium surfactant is a C12/C14 dimethyl benzyl ammonium chloride salt sold under the trade name Dodigen 226, which comprises lauryl dimethyl benzyl ammonium chloride salt and myristyl dimethyl benzyl ammonium chloride salt.
• this compound acts additionally as a grain refiner and prevents nodular growth.
• the quaternary ammonium surfactants further extend the useful current density range, act as grain refiners, and inhibit nodular growth.
• the quaternary ammonium surfactants further extend the current density range because the salts can bind both Sn 2+ and Ag + ions, thus inhibiting diffusion of those metal ions and allowing the plating current density range to be extended.
• the concentration of quaternary ammonium surfactant is between about 0.1 g/L and about 20 g/L, preferably between about 0.8 and about 15 g/L, such as about 0.8 g/L, about 1.6 g/L, or about 2.0 g/L.
• Dodigen 226 may be added to extend the useful current density range, refine the grain size, and prevent nodular growth in the Sn-Ag solder wafer bump.
• Employing too much of the compound causes bath instability and increased nodule formation at the center of wafers.
• the plating rate is limited to low current densities.
• the current densities practically achievable in conventional plating baths are no greater than about 1 ASD.
• Limited current densities adversely affect plating throughput.
• Conventional baths are limited to such low current densities because of rapid diffusion rate of Ag + ions in the bath.
• the electroplating baths of the current invention comprising thiourea compounds, such as HEAT and amidinothiourea, and quaternary ammonium surfactant salts, such as Dodigen 226, can be plated at current densities up to about 20 ASD.
• the increased solubility and stability of Ag + ions in the bath largely remove Ag + ion diffusion rate as an overall rate limiting aspect, and makes it so Sn 2+ diffusion rate is the overall rate limiting aspect. Since the Sn 2+ ion concentration is in the range of about 50 g/L to about 60 g/L, the diffusion rate limited current is much higher.
• the process of the invention employs a current density of greater than about 4 ASD.
• One preferred embodiment employs a current density of greater than 8 ASD, and another preferred high-throughput embodiment employs a current density of more than 10 ASD.
• a source of Sn 2+ ions a source of Ag + ions, an anti-oxidant, and a surfactant.
• the source of Sn 2+ ions may be a soluble anode comprising a Sn 2+ salt, or, where an insoluble anode is used, a soluble Sn 2+ salt.
• the Sn 2+ salt is Sn (CH 3 SO 3 ) 2 (Tin methane sulfonic acid, hereinafter "Sn(MSA) 2 ") in one preferred embodiment.
• Sn(MSA) 2 is a preferred source of Sn 2+ ions because of its high solubility. Additionally, the pH of Sn-Ag plating baths of the present invention may be lowered using methane sulfonic acid, and the use of Sn(MSA) 2 as the Sn source rather than, e.g., Sn(X), avoids the introduction of unnecessary additional anions, e.g., X 2" , into the plating baths, especially those that render Ag + substantially insoluble.
• the concentration of the source of Sn 2+ ions is sufficient to provide between about 10 g/L and about 100 g/L of Sn 2+ ions into the bath, preferably between about 15 g/L and about 95 g/L, more preferably between about 40 g/L and about 60 g/L.
• Sn(MSA) 2 may be added to provide between about 30 g/L and about 60 g/L Sn 2+ ions to the plating bath.
• the source of Ag + ions is limited to salts of nitrate, acetate, and preferably methane sulfonate.
• the concentration of the source of Ag + ions is sufficient to provide between about 0.1 g/L and about 1.5 g/L of Ag + ions into the bath, preferably between about 0.3 g/L and about 0.7 g/L, more preferably between about 0.4 g/L and about 0.6 g/L.
• Ag (MSA) may be added to provide between about 0.2 g/L and about 1.0 g/L Ag + ions to the plating bath.
• Anti-oxidants may be added to the baths of the present invention to stabilize the bath against oxidation of Sn 2+ ions in solution.
• Ag + ions being nobler than Sn 2+
• Sn 4+ can spontaneously oxidize Sn 2+ to Sn 4+ , as explained above.
• This spontaneous redox reaction can cause Ag metal to deposit on the Cu UBM, the walls of the plating tank, or the soluble Sn anode, and to form finely divided Ag metal particles in solution.
• reduction of Sn 4+ which forms stable hydroxides and oxides, to Sn metal, being a 4 -electron process, slows the reaction kinetics.
• HEAT and other thiourea compounds may be added to the bath to prevent the spontaneous reduction of
• antioxidants such as hydroquinone, catechol, and any of the hydroxyl, dihydroxyl, or trihydroxyl benzoic acids may be added in a concentration between about and about, preferably between about 0.1 g/L and about 10 g/L, more preferably between about 0.5 g/L and about 3 g/L.
• hydroquinone may be added to the bath at a concentration of about 2 g/L.
• Surfactants may be added to promote wetting of the under bump metal structure and resist material and enhance the deposition of the wafer bumps.
• the surfactant seems to serve as a mild deposition inhibitor which can suppress three-dimensional growth to an extent, thereby improving morphology and topography of the film. It can also help refine the grain size, which yields a more uniform bump.
• Exemplary anionic surfactants include alkyl phosphonates, alkyl ether phosphates, alkyl sulfates, alkyl ether sulfates, alkyl sulfonates, alkyl ether sulfonates, carboxylic acid ethers, carboxylic acid esters, alkyl aryl sulfonates, aryl alkylether sulfonates, aryl sulfonates, and sulfosuccinates .
• a particularly preferred anionic surfactant is Ralufon NAPE 14-90 (available from Raschig GmbH, Ludwigshafen, Germany) which is a sulfonated ⁇ -naphthol propoxylate/ethoxylate having a block of propylene oxide units bonded to the ⁇ -naphthol hydroxyl group, a block of ethylene oxide units bonded to the propylene oxide block, and a terminal propane sulfonate group.
• Exemplary cationic surfactants include quaternary ammonium salts such as dodecyl trimethyl ammonium chloride, cetyl trimethyl ammonium chloride, and the like.
• non-ionic surfactants include glycol and glycerol esters, polyethylene glycols, and polypropylene glycol/polyethylene glycol.
• Preferred non-ionic surfactants include ⁇ -naphthol derivatives, such as ⁇ - naphtholethoxylates having between 1 and about 24 ethylene oxide monomer units bonded to the ⁇ -naphthol hydroxyl group, more preferably between about 8 and about 16 ethylene oxide monomer units .
• a particularly preferred non-ionic surfactant is Lugalvan BNO12 which is a ⁇ -naphtholethoxylate having 12 ethylene oxide monomer units bonded to the naphthol hydroxyl group.
• the surfactant can be present in the electroplating bath at a concentration between about 0.1 g/L and about 50 g/L, preferably between about 5 g/L and about 20 g/L.
• the electrolytic plating bath of the present invention preferably has an acidic pH to inhibit anodic passivation, achieve better cathodic efficiency, and achieve a more ductile deposit. Accordingly, the bath pH is preferably between about 0 and about 3. In the preferred embodiment the pH of the bath is 0.
• the choice of acids is limited by the poor solubility or substantial insolubility of most Ag salts. Accordingly, the preferred acidic pH can be achieved using nitric acid, acetic acid, and methane sulfonic acid.
• the acid is methane sulfonic acid.
• concentration of the acid is preferably between about 50 g/L and about 200 g/L, more preferably between about 70 g/L and about 120 g/L.
• methane sulfonic acid can be added to the electroplating bath to achieve a bath of pH 0 and act as the conductive electrolyte.
• the electroplating baths of the present invention are preferably employed to plate Sn-Ag alloy solder wafer bumps on Cu UBM in the manufacture of microelectronic devices, such as printed wiring boards (PWB) .
• the plating baths may be used in any application requiring a Sn-based solder wafer bump.
• the plating baths may plate at high rates due to the stability of the bath and the high current densities which may be applied.
• the goal of the process is to yield the product of FIGS. 1 and 2, which is an electronic device substrate with individual solder bumps thereon.
• a first step is substrate preparation.
• the substrate preparation is not narrowly germane to the present invention; but to place the invention in context, it is noted that the invention falls within the following overall context proceeding from substrate preparation through inspection-.
• solder bumps such as SnAg, normally into mushroom shape (bump height varies from about 50 microns to 100 microns)
• the plating solution is preferably maintained at a temperature between about 15°C and about 50 0 C. In one preferred embodiment, the temperature is between about 25°C and about 35°C.
• the substrate is immersed in or otherwise exposed to the plating bath.
• the current density applied is between about 1 A/dm 2 and about 20 A/dm 2 , preferably between about 1 A/dm 2 and about 16 A/dm 2 as described above. At these current densities, the plating rate is between about 1 ⁇ m/min and about 10 ⁇ m/min.
• the thickness of the electrolytically deposited Sn-Ag alloy solder wafer bump is between about 10 ⁇ m and about 100 ⁇ m which, in view of the foregoing plating rates, corresponds to the substrate being immersed in the solution for a duration between about 10 minutes and about 30 minutes.
• the anode may be a soluble anode or insoluble anode. If a soluble anode is used, the anode preferably comprises Sn(MSA) 2 , such that the source of Sn 2+ ions in the plating bath is the soluble anode.
• a soluble anode is advantageous because it allows careful control of the Sn 2+ ion concentration in the bath, such that the Sn 2+ ion does not become either under- or over- concentrated.
• An insoluble anode may be used instead of a Sn-based soluble anode .
• Preferable insoluble anodes include Pt/Ti, Pt/Nb, and DSAs (dimensionalIy stable anodes) . If an insoluble anode is used, the Sn 2+ ions are introduced as a soluble Sn 2+ salt .
• Sn 2+ ions and Ag + ions are depleted from the electrolytic plating solution. Rapid depletion can occur especially with the high current densities achievable with the plating baths of the present invention. Therefore, Sn 2+ ions and Ag + ions may be replenished according to a variety of methods. If a Sn-based soluble anode is used, the Sn 2+ ions are replenished by the dissolution of the anode during the plating operation. If an insoluble anode is used, the electrolytic plating solution may be replenished according to continuous mode plating methods or use-and-dispose plating methods. In the continuous mode, the same bath volume is used to treat a large number of substrates.
• the electrolytic plating compositions according to the present invention are suited for so-called "use-and-dispose" deposition processes.
• the use-and-dispose mode the plating composition is used to treat a substrate, and then the bath volume is directed to a waste stream.
• the use-and-dispose mode requires no metrology; that is, measuring and adjusting the solution composition to maintain bath stability is not required.
• Electroplating baths of the present invention are advantageously stable to spontaneous Ag + ion reduction and can be plated at current densities which are higher than those achievable by conventional plating baths.
• the electroplating baths can be used to plate Sn-Ag alloys having Ag metal content between about 1 wt . % and about 4 wt. %, preferably between about 2 wt. % and about 3 wt . %, the process therefore offering the capability to plate Sn-Ag alloys having a wide range of melting points between about 221°C and about 226°C.
• the Sn-Ag solder wafer bumps are plated with substantially reduced or eliminated voiding between the bump and the Cu UBM.
• the Ag metal is distributed uniformly in the Sn-Ag alloys. This uniformity is important for successful reflow. It also ensures that the bump properties and mechanical strength are uniform across the wafer or other substrate.
• a Sn-Ag bath for electroplating Sn-Ag alloy solder wafer bumps was prepared comprising the following components :
• the bath may comprise 0.5 grams per liter of Defoamer SF.
• the bath precursor is substantially free of surfactant, and the process involves adding the surfactant to the bath precursor after formation of the Ag complex .
• Sn-Ag plating bath comprising the following components:
• Another bath was prepared comprising the following components :
• Another bath was prepared comprising the following components :
• Another bath was prepared comprising the following components:
• Another bath was prepared comprising the following components : 1.5 g Amidinothiourea
• Another bath was prepared comprising the following components :
• N, N 1 -Dimethylthiourea 30 g/L Sn 2+ as 78 g/L Sn(MSA) 2 0.3 g/L Ag + as 0.56 g/L Ag(MSA) 150 mL/L MSA (70% solution) 2 g/L Hydroquinone 8 g/L Ralufon NAPE 1490.
• Another bath was prepared comprising the following components :
• Sn-Ag wafer bumps were plated on Cu UBM using the bath of Example 1.
• the silicon wafer and Cu UBM die pattern was prepared as described above. Un- crosslinked photo resistant material was stripped from the wafer using methylene chloride and ultrasonic agitation for between 30 and 60 minutes.
• Cu metallization was etched by a solution comprising deionized water (60 mL) , ammonium hydroxide (60 mL, 20 to 24% solution) , and hydrogen peroxide (10 mL, 3% solution) .
• Sn-Ag solder wafer bumps were plated from the bath of Example 1 onto dies on patterned silicon wafer. The die positions on the wafer and bump positions within each die are shown in FIGs.
• FIGs. IA, IB, 1C are SEM photographs showing the Sn-Ag solder wafer bumps as deposited at 20Ox, 80Ox, and 300Ox magnification, respectively. For each measurement technique, 5 bumps (bump pattern shown in FIG.
• 3B and designated I 1 2 ⁇ , 3_, 4_, and 5_ in the horizontal axes in Tables I and II below) were analyzed at each of 3 die positions (die pattern shown in FIG. 3A and designated 3, 6, 7 in the vertical axes in Tables I and II below) .
• FIGs. 2A, 2B, 2C are SEM photographs showing reflowed Sn-Ag solder wafer bumps as deposited at 20Ox, 80Ox, and 300Ox magnification, respectively.
• the reflowed bumps are smooth and show a uniform ball shape, and demonstrate zero voiding.

Landscapes

• Engineering & Computer Science (AREA)
• Computer Hardware Design (AREA)
• Chemical & Material Sciences (AREA)
• Power Engineering (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Manufacturing & Machinery (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Condensed Matter Physics & Semiconductors (AREA)
• Electroplating Methods And Accessories (AREA)
• Electroplating And Plating Baths Therefor (AREA)
• Electric Connection Of Electric Components To Printed Circuits (AREA)
• Die Bonding (AREA)

Priority Applications (5)

Applications Claiming Priority (4)

Publications (2)

Family

ID=37743065

Family Applications (1)

Country Status (7)

Cited By (1)

Families Citing this family (30)

Citations (2)

Family Cites Families (26)

• 2006
  • 2006-08-09 US US11/463,355 patent/US7713859B2/en active Active
  • 2006-08-14 CN CN2006800378536A patent/CN101622701B/zh active Active
  • 2006-08-14 JP JP2008527028A patent/JP5207968B2/ja active Active
  • 2006-08-14 EP EP06801412A patent/EP1946362B1/en active Active
  • 2006-08-14 KR KR1020087006190A patent/KR101361305B1/ko active IP Right Grant
  • 2006-08-14 WO PCT/US2006/031618 patent/WO2007022075A2/en active Application Filing
  • 2006-08-14 AT AT06801412T patent/ATE541306T1/de active

Patent Citations (2)

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events